As a general example of a system configuration, an air pollution control apparatus of a boiler for thermal power plant or chemical plant is disposed in order of denitrification equipment in a flue gas flow channel, an air-preheater air heater, a heat recovery unit of reheating gas-gas heater, a dry electronic precipitator, wet desulfurization equipment, a reheating unit for the gas-gas heater, and a chimney. Here, the gas-gas heater is configured such that the heat recovery unit and the reheating unit are connected to a cool and hot water circulating line to perform a heat exchange with a flue gas through a circulating pump using water as a medium.
In this control apparatus, the flue gas of the boiler is guided to the air heater to be cooled to a temperature of, for example, 130 to 150° C. by exchanging heat with combustion air and then is guided to the heat recovery unit of the gas-gas heater to be further cooled. Thereafter, after the flue gas is guided to the electronic precipitator to remove fly ashes, a high-temperature flue gas in an outlet of the electronic precipitator is further cooled to a low temperature by exchanging heat with water and then is guided to the wet desulfurization equipment. In the wet desulfurization equipment, SO2 contained in the flue gas is absorbed and removed by absorber which is prepared by dissolving, for example, limestone in the form of slurry and remaining fly ashes in the flue gas are also removed in the gas-solution contact process. Then, the flue gas in which SO2 and the fly ashes are removed is guided to the reheating unit of the gas-gas heater. Here, the temperature of the flue gas temperature-dropped by SO2 absorber and the like in the treatment process of the wet desulfurization equipment is raised by the heat exchange with heat medium water passing through an interior of a pipe disposed in the reheating unit of the gas-gas heater. This causes functions of preventing white smoke generation due to a reduction of the amount of water condensation and improving diffusion efficiency due to temperature rise, when the flue gas is released from the chimney to an atmosphere.
For example, a fin tube heat exchanger has been proposed as a heat exchange method of large-scaled heat recovery unit and reheating unit of the gas-gas heater in coal-fired power plant (Patent Literature 1).